In this lesson, students experience the historical discovery of fossils which increasingly link whales to earlier land-dwelling mammals. This experience also reveals how scientists can make predictions about past events based on the theory that whales evolved from certain groups of early land mammals. Such predictions suggest the age and location of sediments where fossils of early whales would most likely be found and even their traits. This lesson also provides confirmation, with multiple independent lines of evidence, that there is a series of intermediate forms showing a gradual accumulation of changes that link certain terrestrial mammal groups with modern whales.